so we come to see our genetics and the environment that we have it as partners. and so that's our new scientific understanding. but we don't regulate chemicals on the basis of whether or not they alter the way a brain cell migrates during early infancy which could lead to a learning disability, for example. >> one of the most harmful toxins is atrazine. one of your peers at the university of california berkeley, dr. tyrone hayes, who is featured in your film "living downstream,." and he says, quote, "there's almost no aquatic environment, including rain water, that's atrazine free." here he's speaking about that toxin. >> so, this is darnell. darnell is going to be famous. he's the first genetic male frog that actually completely turned into a female upon exposure to atrazine. so he's been exposed to atrazine at one parts per billion at tadpole stage. and now he's an adult male that mates with other males and that actually lays eggs. so he's a functional female. he may very well be a hermaphrodite if we dissect him. but he's a functional female, anyway. and he ha